The sodium salt of the dye described herein is known as Acid Red 151, Color Index No. 26,900. It is very effective for dyeing synthetic fibers, especially nylon. It is necessary to employ water miscible solvent(s) to aid in dissolving this disazo dye so that it will be in acceptable form for transport and use. Usually, transported solutions will have about 15% to 25% dye in solution.
Problems can arise, however, even though dye solubility is achieved for shipping and handling. For instance, when the dye liquid is diluted with additional water prior to use in a dyeing operation, the dye itself often comes out of solution. In some cases, it comes out of solution in the form of a gel, a solid phase colloidal solution. Once formed, such a gel can block transfer lines and can be very difficult to remove. The invention provides a way of overcoming this difficulty by eliminating the gelling tendency of this particular disazo dye. With the concentrated dye-surfactant solutions of this invention, water dilution of the dye concentrate results in a desirable nongelling fluid dispersion of the dye which can be handled easily.